First mobs (@ 17:00 mark), packs with Volatile energy sha's, those seem to explode dealing aoe damage, coupled with RNG breath thingy from the other mobs, if timed "correctly" then the fecal matter hits the rotating cooling device (almost wiped last nite with a 2 melee + tank setup) on those.
Second set of mobs (@ around 26:00 mark) I reached red health and the 2 melee dps died.

Granted, the healer was new to the instance, but is there something that can be done to lessen the overall damage short of using CC? (I'm hesitant to rely on PUG's ability to respect/not break it)

yes i had the same problem but there is nothing you can do other then ofcourse using your cooldowns.
it will get a lot easyer when we get better gear but for now my healer had to drink after each pac of trash

also you cna use tyboom + ursols vortex as damage reduction technique if you knock the mobs away and then put up a vortex so they cant reach you

As a guardian, you have at least two ways to interrupt: Skull Bash and Bear Hug. I myself have also specced for Mighty Bash, because I find it highly useful in dungeons and world PvP. Use these abilities to interrupt the dark flames as fast as possible, because they do a lot of damage, and always assume dps will just keep on facerolling instead of interrupting. Keep these mobs facing away from other party members, as you should do with almost any kind of mob. Pool your rage a bit towards the end of the battle for some nice Frenzied Regeneration heals for those little pests that explode.

As a healer I concur that those packs are quite tough with any tank. I've not had to drink inbetween the packs, but I do see how an unexperienced healer might panic and use more expensive heals and then struggle for mana.

The key, I think, is not to be afraid to use cooldowns (this goes for both healer and tank) and prioritize the tank over reckless melee DPS, who have to learn to pay a little more attention. If your healer wasn't using their tank cooldowns like Hand of Sacrifice, Pain Suppression, Void Shift, Lay on Hands, or simple Nature/Ancestral Swiftness macroes, then that might have been a part of the issue. Perhaps next time try to remind them gently that there is nothing to save those buttons for.

Maybe could be a issue with disc priests (my healer that run) and multiple target healing, I have had 4-5 other runs with other classes of healers and it was visibly less hectic (I tank with VuhDo addon on, it's nice to have it's functionality and gives a good overview of the group)

At first, I thought the trash was really rough (probably is the roughest heroic 5man trash still), but after dealing with it multiple times, it's not too difficult.

First things firsts: use your survival cooldowns! The next boss really doesn't require much in the ways of cooldowns (unless you're doing the achievement), so feel free to use them.

Another thing I've seen other tanks fail to do: ensure that the adds are facing towards you and not the rest of the group. It can really stress out a healer when more than one person is taking excessive damage, and it's generally easier to heal just the tank. Sometimes you can help some random people standing in the wrong spots, but do the best you can. I haven't done extensive testing on the "breath" mechanic (since I love building Vengeance and my healer is usually bored), but it may be possible to outrange it, since I'm fairly certain it will turn to face you... I'll report back the next time I run the instance and see if either apply.

Onto the little things... yes, we have Bear Hug and Skull Bash to interrupt casters, but we also have talents! I personally use Typhoon (especially in conjunction with Ursol's Vortex at many times) to get melee out of my face, range pull something when I'm on the move, and interrupt casters when I don't have other options. Sometimes you or party members can use racials to your advantage, such as Warstop for Taurens or Arcane Torrent for BE's. Also, especially if you're in a group with someone you know, get them to target a specific add to ensure it is CC'd.

I haven't had a chance to test it properly, but don't the Shadow-Pan arrow fire puddles on the ground hurt the mobs as well? I know they hurt players, but I've seen non-aggro'd groups sitting in puddles not at full health. If so, that's 15k damage a tick, a little extra DPS to help eliminate them.

*edit* - Forgot to mention, save those Volatile adds for last and pray you do not have a DPS AoEing them down on purpose. Those little adds are there as a hint: focus down the individual mobs or go boom!

One tip I have: Mark the Destroying Sha with skull/x/etc and people will generally focus them down instead of going max DPS AoE mode 9000. The rest of the mobs in those packs are pretty bland (the volatiles explode, the regenerators regenerate, the other ones enrage). But yeah, use any of your short CDs freely, and your longer ones if it seems reasonable/necessary. If you really want to help your healer, you can always use Heart of the Wild and spam Rejuv on yourself/the melee.

As a healer I concur that those packs are quite tough with any tank. I've not had to drink inbetween the packs, but I do see how an unexperienced healer might panic and use more expensive heals and then struggle for mana.

The key, I think, is not to be afraid to use cooldowns (this goes for both healer and tank) and prioritize the tank over reckless melee DPS, who have to learn to pay a little more attention. If your healer wasn't using their tank cooldowns like Hand of Sacrifice, Pain Suppression, Void Shift, Lay on Hands, or simple Nature/Ancestral Swiftness macroes, then that might have been a part of the issue. Perhaps next time try to remind them gently that there is nothing to save those buttons for.

Not really. If dps (and possibly the tank) are being dumb the healer is going to have to drink regardless of skill. Single targetting the mobs is what should be happening not going balls to the wall on your aoe dps. Using your mana efficient heals while popping cooldowns is going to work if that isn't happening. And cooldowns you know have cooldowns and there is more than 1 pack.

First mobs (@ 17:00 mark), packs with Volatile energy sha's, those seem to explode dealing aoe damage, coupled with RNG breath thingy from the other mobs, if timed "correctly" then the fecal matter hits the rotating cooling device (almost wiped last nite with a 2 melee + tank setup) on those.
Second set of mobs (@ around 26:00 mark) I reached red health and the 2 melee dps died.

Granted, the healer was new to the instance, but is there something that can be done to lessen the overall damage short of using CC? (I'm hesitant to rely on PUG's ability to respect/not break it)

Why would you be against CC? If PUGs break it, then deal with it then. You are no worse off than before. If they don't break it, it makes those pulls cake.

Not really. If dps (and possibly the tank) are being dumb the healer is going to have to drink regardless of skill. Single targetting the mobs is what should be happening not going balls to the wall on your aoe dps. Using your mana efficient heals while popping cooldowns is going to work if that isn't happening. And cooldowns you know have cooldowns and there is more than 1 pack.

Yes, there is indeed more than one pack, but in my experience the tank doesn't come into critical health range more than once or twice per the whole time. Yeah I've had some pretty crap tanks, they still didn't die. Void Shift, Guardian Spirit and Serendipity mechanic were enough to keep them afloat. So really, I disagree with what you said.